Decad as vesica piscis

Here we see another form of the Pythagorean decad, highlighting its hexagonal nature.

Geometries such as this have been used by people throughout history—Pythagoreans, Freemasons, &c.—to justify decimalism. This is a false understanding of the decad. In both this diagram, as well as in the Tetractys, it is clear that the fundamental organizational principle is hexagonal, not decadian. The concept of ten emanates from the underlying reality of the hexagon—not the other way around.